Such a control system is known from DE-PS 1 165 645. The inlet and the outlet solenoid valve are designed as simple, separate solenoid valves, each of which is followed by a restrictor as the releasing or braking nozzle. The relay valve designed separately from these solenoid valves is supplied with compressed air from the main reservoir pipe via a non-return valve, the volume of the control chamber pressurizing the piston is enlarged by a separate air reservoir, and a throttle is arranged as a passage monitoring element in a connection from the main air pipe to this air reservoir. The result of the constantly opened, throttled connection between the main air pipe and the control chamber is that, while controlling the pressure in the control chamber by means of the solenoid valves, the control chamber pressure can be falsified by the air inflow or outflow from or to the main air pipe, so that accurate position control of the desired control chamber pressure, and thus, via the relay valve of the main air pipe pressure, cannot be assured.
Another special feature of this known control device is that, when emergency braking is initiated, with a correspondingly rapid pressure drop in the main air pipe due to the throttled connection in the control chamber, the pressure drop is merely delayed; thus, the relay valve responds in the direction to refeed the main air pipe pressure from the main reservoir pipe, and emergency braking is delayed or even cancelled. The same applies when filling strokes are introduced into the main air pipe, during which the relay valve of the known control system would respond and would bring about undesired venting of the main air pipe.
To eliminate these deficiencies, it could be obvious to bridge the restrictor in the connection from the main air pipe to the control chamber of means of a solenoid valve, which is open in the quiescent state of the control system and is closed only when the inlet or outlet solenoid valve is actuated. As a result, in the quiescent state of the control system the connection between the control chamber and the main air pipe would not be throttled, thus obviating an undesired response of the relay valve during emergency braking or filling strokes. However, owing to the additional solenoid valve the cost of construction and in particular the energy consumption of the control system is significantly increased. For long trains with a plurality of such electropneumatic control systems this would require an acceptably large amount of current fed into the electric control lines, and thus would not be usable precisely in those train formations in which such control systems would be especially necessary and advantageous.
As a consequence of the separate arrangement of the individual elements, the known control system requires a great deal of time to build and assemble.